An arrangement of an air filter and a carburetor is disclosed in German patent publication 2,902,348. The membrane carburetor includes an arrangement for compensating for pressure fluctuations of the ambient pressure on the fuel-filled control chamber of the carburetor. A compensation chamber is arranged on the dry rear side of the control membrane. The compensation chamber communicates with a compensation channel which branches from a flow compartment at atmospheric pressure. With this arrangement, a reliable operation of the engine is ensured. The combustion air flows through the intake channel section of the membrane carburetor into the combustion chamber of the engine. This combustion air mixes with fuel entering into the intake channel section from the control chamber. In this way, an underpressure develops in the control chamber whereby the control membrane is moved and a control valve is opened via which fuel flows into the control chamber. Fluctuations of the ambient pressure operate via the compensation chamber on the control membrane so that more or less fuel is metered in dependence upon ambient air pressure. An overmetering or undermetering of fuel into the intake channel of the membrane carburetor is thereby avoided. The known arrangement is large and is complex to assemble.
It is an object of the invention to configure the compensation of a membrane carburetor in a simple manner in an arrangement of air filter and membrane carburetor so that the degree of contamination of the air filter is considered while, at the same time, facilitating a simple manufacture and assembly. The air filter is connected ahead of the membrane carburetor.
The invention is for a combination of an air filter and a membrane carburetor. The combination includes: a carburetor housing defining an air intake channel through which a stream of air is drawn by suction; the carburetor housing further defining an interior space; a membrane partitioning the interior space into a control chamber for holding fuel and a compensation chamber; fuel-conducting channels extending from the control chamber and opening into the air intake channel for conducting fuel from the control chamber to the air intake channel for entrainment by the stream of air; an air filter housing defining a flow space; a connecting pipe connecting the flow space to the air intake channel for conducting the stream of air from the flow space to the air intake channel and the connecting pipe having an opening in the flow space where the stream of air enters the connecting pipe; a compensation channel for connecting the compensation chamber to the flow space; the compensation channel including a channel segment within a portion of the connecting pipe and the channel segment having an opening in the flow space; the connecting pipe having a wall and a part of the wall defining a wall of the compensation channel in the region of the channel segment; and, the openings of the connecting pipe and the channel segment of the compensation channel being disposed in the flow space in respectively different planes.
A simple assembly of the compensation unit is possible because of the configuration and arrangement of the compensation channel in the connecting piece between the intake channel section of the membrane carburetor and the flow space. The compensation channel opens into the housing, especially the air filter housing. This housing forms the flow space. Because of this constructive measure, a part of the wall of the connecting piece simultaneously forms a wall of the compensation channel. The housing, which forms the flow space, is purposefully partitioned by an air filter element. The respective openings of the connecting piece and the compensation channel lie on the clean air side of the flow space. The connecting piece extends through the air filter element together with the compensation channel guided therein. The air filter element and a filter carrier for accommodating the air filter element are thereby only penetrated at one location.
The plane defined by the opening of the compensation channel lies in a plane other than the plane defining the opening of the connecting piece itself. Preferably, the planes of both openings are arranged at different elevations or are perpendicular to each other. In this way, it is ensured that no dynamic pressure is present at the opening of the compensation channel. Instead, static pressure is present at this opening.
With increasing contamination of the air filter, the underpressure increases on the clean air side of the housing during operation of an internal combustion engine supplied by the membrane carburetor. In this way, the problem of an overenrichment of an air/fuel mixture is present. To counter this problem, the underpressure of the clean air side of the flow space or of the housing is present on the dry side of the control membrane via the compensation channel and operates in a compensating manner on the control membrane of the membrane carburetor. This leads to the situation that the air/fuel mixture remains substantially constant in the mixture ratio even when contaminants have accumulated on the air filter.
If the opening of the compensation channel is arranged in the flow space at a different topographical elevation to the opening of the connecting piece for the combustion air, the opening of the compensation channel can be placed in a peripheral region of the housing defining the flow space. In this way, it is ensured that only static pressure is present at the opening of the compensation channel.
It can be purposeful to configure the connecting piece and the compensation channel as one piece with the housing defining the flow space. To exchange an air filter element, the housing is partitioned into two housing parts in the plane in which the air filter element is mounted or is partitioned into two housing parts in a plane parallel thereto. The compensation channel and the connecting piece can preferably be configured as one piece with an interior element of the air filter housing and extend through the air filter at one location.
The interior element is, in plan, preferably circularly shaped with a cylindrical rim. The cylindrical rim is configured so as to have a U-shape when viewed in section and engages over a corresponding annular flange of a flow space in the air filter housing part which is connected to the output channel section of the membrane carburetor so as to permit flow. The base of the circularly-shaped interior element supports a cylindrically-shaped end section of the connecting piece. The end section projects the same distance to both sides. The end section of the compensation channel extends through the base of the interior element in the end section of the connecting piece and this end section of the compensation channel opens in a widening cone on its inner side in the region of the base. In the assembled condition of the interior element, the end section of the compensation channel sits with the cone on a conical connecting end of the compensation channel in the air filter housing. In this way, a tight separation between the compensation channel and the connecting piece is ensured.
The free end of the compensation channel on the support element is provided with a diaphragm arranged at the opening of the compensation channel. The diaphragm has a central, preferably circular, opening. The diaphragm is advantageously made of metal and can be seated in the opening of the compensation channel. Different diaphragms make possible the adaptation of the compensation device to different kinds of membrane carburetors. If the central opening is to be very accurate, the diaphragm is preferably made of metal, especially as a turned piece.
It is purposeful to provide flanges at the outer side of the air filter housing for connecting the compensation channel and the connecting piece. The seal of the sealing surfaces at the flanges is assumed by profile seals or roll rings made of elastic material.
At the opening of the connecting piece in the flow space, it is advantageous to fix a flow straightener, such as a lattice, for the purpose of attenuating the noise of the air sounds in the connecting piece. The flow straightener is advantageously so configured that it subdivides the clear cross section of the connecting piece into the intake channel and the compensation channel.